Measuring airflow at the fan inlet presents challenges from a measurement technology stand point. Achieving accurate flow measurement at the fan inlet, without affecting fan performance, is an important consideration when selecting the correct meter. The large variation in airflow velocity as well as the multiple fan configurations that exist within an AHU must be taken into consideration. Measuring airflow at the fan inlet can be advantageous from an accessibility stand point as well as the advantage of monitoring the performance of fan walls at the source.